Metallic gasket

ABSTRACT

A metallic gasket comprising a base plate having a first thickness-increased portion  3  formed at a peripheral edge on a combustion chamber opening  3  side of a base plate, and a first seal line SL 1  and a second seal line SL 2  arranged on the outer side of said first thickness-increased portion  3.  No openings other than a cooling water hole  8  exist between said two seal lines. Beads formed along said seal lines SL 1  and SL 2  each consist of a convex metal bead raised only upward from an upper surface of said base plate and a rubber bead made of an elastic sealing material fixed to a convex portion and a concave portion of said metal bead. This structure of said metallic gasket can improve a processing accuracy of said metal bead and also enhance cooling effects on said metallic gasket itself and said joint surfaces of an engine, between which said metallic gasket is disposed.

This application is a national stage entry of international applicationno. PCT/JP02/11793, filed on Nov. 12, 2002, the entire specification,claims and drawings of which are incorporated herewith by reference.

TECHNICAL FIELD

The present invention relates to a metallic gasket and more particularlyto a metallic gasket which is sandwiched in a joint between the jointsurfaces of a cylinder block and a cylinder head of a water-cooledinternal combustion engine, and which is capable of improving thecooling effect of the joint and the gasket itself.

BACKGROUND ART

Among conventional metallic gaskets aimed at improving the coolingeffects of the parts between which a metallic gasket is sandwiched,there is one which is described in Japanese Patent Laid-Open No.60-3465.

As shown in FIGS. 21 and 22, this metallic gasket comprises a base plate50 made of a thin, high-rigidity, elastic metal plate having a firstmetal bead 52 formed along a seal line SL1 encircling the innerperipheral edge of each combustion chamber opening 51. In the base plate50, on the outer side of the first metal bead 52, a second metal bead 55is formed along a seal line SL2 encircling cooling water holes 53 butseparating and not encircling bolt holes 54. Reference numeral 56denotes an oil hole, and a third seal line SL3 is formed encircling theinner peripheral edge of the oil hole 56.

When the metallic gasket is mounted at the joint between the jointsurface of a cylinder block 60 and the joint surface of a cylinder head61 and fastened with bolts, the metal beads 52, 55 are elasticallydeformed according to a fastening force, a combustion gas of thecombustion chamber bore 51 is line-sealed by the first metal bead 52 anda gap space S at a minute height, to which only the cooling water holes53 are open, is formed between the two metal beads 52, 55. Cooling wateris pressure-fed through the cooling water holes 53 into the gap space Swhen the engine is running, and as a result of cooling watercirculation, the joint surfaces and the metallic gasket itself arecooled. Also by the pumping action of vibration amplitude caused byexplosion of the combustion gas, the flow of cooling water to the gapspace S is promoted.

The minute gap of the gap space S is formed by a balance of the axialtension of the clamping bolts of the engine with the urging force of themetal beads 52, 55 that resist the fastening. Since a line seal by metalis applied, it is necessary to set a high gasket factor to secure adesired sealing property, so that the axial tension of the bolts must beset on a higher side, and the gap tends to become small.

Further, the cubical expansion of the engine occurs by the heat ofengine operation, increasing the fastening pressure, and as thetemperature rises, the above-mentioned gap decreases. Progresses havebeen made in reductions in size and weight, technical sophistication,and energy saving of the engine, and aluminum has come to be used ingreater quantities as material for the engines. As a result of increasedexpansion coefficient by a difference of materials, there is a tendencythat it is becoming difficult to secure the above-mentioned gap.

Further, in the bead structure of the above-mentioned gasket, asdescribed above, the metal beads 52, 55 formed in the base plate 50 needto generate a high surface pressure. Therefore, it is necessary to adopta material of high hardness, and in hard materials, internal stressconcentrates in the portions of bending radius of the metal beads 52,55, and when subjected to repetitive stress by vibration amplitude, theyare liable to fatigue failure, and gasket lifetime is shortened.

Supposing an engine is made by aluminum, casting of aluminum isdifficult and blowholes occur in casting. Therefore, when processing thejoint surfaces, adjacent blowholes on the joint surfaces are sometimesconnected. At this time, the conventional beads 52, 55 are for linesealing and come into metal-to-metal contact with the joint surfaces,and therefore the blowholes may stretch, running across the line-sealedbead line, or the seal line may be displaced during operation due to anexpansion difference between materials of the gasket and the engine,resulting in the beads 52, 55 being located on the blowholes, increasingchances of water leakage. An aluminum-made engine is liable to dents intransit. Those dents may give rise to the above-mentioned phenomena.

Further, since the base plate 50 needs to be formed by a material ofhigh hardness, it is difficult to improve the processing accuracy of themetal beads 52, 55 formed by bending the base plate 50.

Among other conventional metallic gaskets, there is one which isdisclosed in Japanese Patent Laid-Open No. 2001-173791.

As shown in FIG. 23, this metallic gasket comprises two base plates 50.In other words, a thickness-increased portion 52 is formed at the innerperipheral end of the combustion chamber opening 51 side of the thickerbase plate (the upper base plate) out of the two base plates 50, convexbeads 53 are formed on the base plates 50, each on the outer side of thethickness-increased portion 52 and at a height higher than the thicknessof the thickness-increased portion 52, and the two base plates 50 arelaminated in such a way that the convex sides of the base-plate beads 53face each other. Further, an elastic sealing material 54 is filled inthe outside-facing concave portions of the metal bead 53.

The metallic gasket is disposed between the opposing joint surfaces ofthe cylinder head and the cylinder block, and when they are fastenedtogether, the base-plate beads 53 are compressed and deformed until thethickness-increased portion abuts on the opposite base plate at theperipheral edge of the combustion chamber opening, concurrently withwhich, the elastic sealing material parts 54 filled in the concaveportion are compressed and deformed, and consequently a combustion gas,oil, and cooling water are sealed by a sealing pressure from a combinedspring including the spring force of the base-plate beads 53 and thespring force of the elastic sealing material parts 54. Needless to say,some of the conventional metal beads have no elastic sealing materialfilled in their concave portion and some conventional metal beads areformed by a single piece of base plate.

In this conventional metallic gasket, when the base-plate beads 53 andthe elastic sealing material parts 54 are deformed when the bolts aretightened, they cooperate to generate a resilience to thereby generate arequired sealing pressure along the seal lines.

However, when the base plate 50 is formed of metal plate of low hardnesswith a view to preventing fatigue failure of the base-plate beads 53 andreducing production cost, in the above-mentioned metallic gasket, whenthe bolts are fastened and the elastic sealing material 54 in theconcave portion is deformed under compression, an external force acts todeform the base plate 50 and the base-plate beads 53 to warp in thethrough-thickness direction. When the base plate 50 is made of metal oflow hardness as mentioned above, the bead shape-preserving power is lowand the base plate deformation resistance is weak, so that the sealingproperty is reduced accordingly.

By repeated load by repetition of operation and stoppage of the engine,after a long period of use, problems arise, such as a decrease in axialtension of the clamping bolts, changes with time of the base-plate bead53 on the base plate 50, or deterioration in the elastic sealingmaterial 54 of the concave portion of the bead; therefore, the sealsurface pressure is likely to drop. Such problems tend to come upparticularly at overhanging parts on the outer side of the clampingbolts.

When the elastic sealing material 54 is formed by baking in the concaveportions of the base plates, even if the elastic sealing material 54 athigh temperature is filled in the concave portions, it changes in volumeby an amount of thermal expansion during subsequent open cooling, thecenter portion of the elastic sealing material 54 where the thickness isat its highest contracts by an amount of thermal shrinkage. This isdisadvantageous when the surface pressure decreases as described above.Such a phenomenon as this seems to be likely to occur particularly whenthe gasket is mounted in the engine which has been assembled with a weakfastening axial tension.

DISCLOSURE OF THE INVENTION

The present invention has been made with the above problems in mind, andhas as its task to provide a metallic gasket capable of improving theprocessing accuracy of metal beads, and enhancing the cooling effects onthe metallic gasket itself and the joint surfaces in which the metallicgasket is mounted.

To solve the above problems, the invention set forth in claim 1 relatesto a metallic gasket comprising a base plate made of a thin metal plate,the base plate having at least a combustion chamber opening and acooling water hole, and having a first thickness-increased portion madeof metal and increased in thickness and encircling a peripheral portionof the combustion chamber opening, a first bead formed on the outer sideof the first thickness-increased portion of the base plate in a mannerto endlessly encircle the combustion chamber opening, and a second beadformed on the outer side of the first bead in a manner to endlesslyencircle the combustion chamber opening and the cooling water hole,wherein in a region of the base plate between the first bead and thesecond bead, there are no holes other than the cooling water hole, andeach of the first and second beads is a composite bead of a metal beadand a rubber bead, wherein the metal bead is formed only on one surfaceof the base plate by bending the base plate in a through-thicknessdirection to create a convex portion higher than the height of the firstthickness-increased portion, wherein the rubber bead is formed of anelastic sealing material fixed to the convex portion side surface of themetal bead and filled in a concave portion on the reverse side of theconvex portion and the rubber bead is compressed and deformed in thethrough-thickness direction in cooperation with the deformation of themetal bead, and wherein the elastic sealing material on the surface ofthe convex portion side is fixed at least to the surface of the convexportion of the metal bead and is arranged to have a height equal orsubstantially equal to the height of the metal bead.

Incidentally, it is desirable to limit the largest width of the rubberbead on the convex portion side within 1.5 times the width of the metalbead with the exception of the bolted portions which are subjected to alarge pressure. It is necessary to apply more load to the base platewhere the rubber bead has a larger width. From a viewpoint of inhibitingan increase in load, it is desirable to limit the width of the bead ofan elastic sealing material within 1.5 times the width of the metal beadas mentioned above. This does not apply to where large load is to beapplied locally.

According to the present invention, the first thickness-increasedportion made of metal receives most of the fastening surface pressureand seals a combustion gas of high pressure. Cooling water that flowsthrough the cooling water hole into and out of a gap space between thefirst bead and the second bead is sealed by a composite spring force ofa spring force of the metal bead higher than the height of thethickness-increased portion and a spring force by the elasticdeformation of the rubber bead formed on both surfaces of the metalbead.

At this time, since the compression-deformed amount of the beads isregulated by the first thickness-increased portion, a gap space by a gapgreater than before is formed between the first bead and the secondbead, and consequently the cooling effect on the metal bead and so on isincreased.

At this time, the bead according to the present invention applies a sealby a composite spring force of the metal bead and the rubber bead, andsince the seal surface of the beads that contact the opposing jointsurface is formed by an elastic sealing material, the gasket factor issmall, so that the joint can be sealed with a low surface pressure andno problem arises even if the compression-deformed amount is regulatedas mentioned above.

Because the sealing surface is formed by the elastic sealing material,even if there are blowholes on the joint surfaces, a satisfactorysealing can be achieved to prevent water leakage.

The rubber bead is soft and adapts itself to the joint surfaces and iscapable of accommodating the processed surface roughness andsatisfactorily sealing the flaws that occur in transit.

Because a small gasket factor can be adopted for the bead as mentionedabove, the hardness of the base plate used for metal beads can be set ata low value. For example, with an intention of providing inexpensivegaskets, plated soft steel may be adopted instead of high-hardnessstainless steel. The amount of elastic sealing material used is smallbecause it is used only on the upper and lower surfaces of the beadlines for sealing.

The metal beads are required only slightly higher than the height of thefirst thickness-increased portion, and the height of the rubber beads isset so as to be equal or slightly higher than the height of the metalbeads in designing the mold, and therefore the processing accuracy isstable. If the height of the metal beads is 30% higher than the firstthickness-increased portion, the elastic sealing material does notsuffer deformation fracture, generated load is a composite force of themetal beads of soft steel and the soft rubber beads and is therefore notstrong, and there is not such a large loss of load as to affects thesealing against the combustion gas pressure.

The invention is also characterized in that a second thickness-increasedportion is provided at an outer peripheral edge of the base plate.

According to the present invention, most of the fastening surfacepressure is received by the two thickness-increased portions made ofmetal. In the additional presence of the thickness-increased portion atthe outer peripheral edge of the base plate, the compression-deformedamount of the beads can be set stably at a specified value.

The invention is also characterized in that to equalize the surfacepressure when the gasket is mounted between the joint surfaces, theheight of the first thickness-increased portion is varied partly andthat the height of the second thickness-increased portion is lower thanthe lowest height of the first thickness-increased portion.

According to the present invention, as a result of the sealing pressurebeing equalized by the first thickness-increased portion, the boltfastening force can be utilized efficiently. Equalizing the sealingpressure in the circumferential direction at the inner peripheralportion of the combustion chamber opening means that the pressure tothat portion of the joint surface which is the first thickness-increasedportion at the inner peripheral portion of the combustion chamberopening is also equalized circumferentially, thereby preventing theshape distortion of the bore on the joint surface by the sealingpressure at the first thickness-increased portion. If the shape of theopening on the joint surface is deformed, or distorted, this leads topower loss or oil consumption increase.

In the first and second thickness-increased portions that receive agreater part of the bolt fastening force, by setting the secondthickness-increased portion to a relatively lower thickness, it becomespossible for the largest load to be applied to the firstthickness-increased portion, thereby generating a high sealing pressure.

The invention is also characterized in that the firstthickness-increased portion is formed by folding back the peripheraledge on the combustion chamber opening side of the base plate, and ashim is fitted into the folded portion to thereby adjust the height ofthe first thickness-increased portion.

According to the present invention, it becomes possible to lower thehardness of the base plate as described above, and therefore forming thefirst thickness-increased portion by bending becomes easier and itbecomes possible to adjust the height of the first thickness-increasedportion by means of a shim.

When the second thickness-increased portion is formed by bending, by theabove mentioned insertion of a shim, it becomes possible to set thesecond thickness-increased portion to a lower height than the height ofthe first thickness-increased portion without subjecting the secondthickness-increased portion to forging.

The invention is also characterized in that the firstthickness-increased portion is formed by folding back the peripheral endon the combustion chamber opening side of the base plate, and a leafspring for spring action in the through-thickness direction is insertedin the folded portion.

According to the present invention, by imparting elasticity by the leafspring to the whole or a part of the first thickness-increased portion,the surface pressure in the circumferential direction can be equalizedeasily, and by providing the first thickness-increased portion with thespring, the first thickness-increased portion can follow after thethermal deformation that occurs during engine operation, andconsequently the surface pressure equalization takes places in the firstthickness-increased portion in a manner to follow after the thermaldeformation.

The invention is also characterized in that by partly varying at leastone of the height of protrusion and the width of the beads in theextending direction thereof, the sealing surface pressure by the beadsis equalized in the extending direction thereof.

The invention is characterized in that a thin corrosion-resistant filmis also fixed to that portion of the base plate located between thefirst bead and the second bead and at least on the surface of the convexportion side of the metal beads on the base plate.

The invention is also characterized in that one or not less than twoseal lines are arranged on at least one of the surface of the elasticsealing material fixed to the surface of the convex portion side and thesurface of the elastic sealing material filled in the concave portion,the sealing material being used to form the rubber beads.

The invention is also characterized in that one line or not less thantwo lines of protrusions are provided where the sealing pressure isrelatively low on at least one of the surface of the elastic sealingmaterial fixed to the surface of the convex portion side and the surfaceof the sealing material filled in the concave portion of the base plate,the sealing material being used to constitute the rubber beads.

The invention is also characterized in that in the above-mentioned linesof protrusions, at least one of the height of protrusion and the widthin the extending direction thereof is varied according to the sealingpressure at formed positions the protrusions, and at least one of theprotrusion height and the width is set at a larger value where thesealing pressure is lower.

The invention is also characterized in that a plurality of protrusionsare provided on at least one of the surface of elastic sealing materialfixed to the surface of the convex portion side and the surface of theelastic sealing material filled in the concave portion of the beads, andin the plurality of protrusions, at least one of an area per height ofprotrusion and a unit length is varied according to the sealing pressureat formed positions of protrusions.

The invention as set forth wherein a plurality of base plates arestacked in a multilayered structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is plan view for explaining a metallic gasket according to afirst embodiment of the present invention.

FIG. 2 is a sectional view taken along the line A—A in FIG. 1.

FIG. 3 is a sectional view taken along the line B—B in FIG. 1.

FIG. 4 is a sectional view for explaining another mode of embodying afirst thickness-increased portion.

FIG. 5 is a sectional view for explaining yet another mode of embodyingthe first thickness-increased portion.

FIG. 6 is a diagram for explaining another mode of embodying a bead.

FIG. 7 is a sectional view for explaining a still other mode ofembodying the first thickness-increased portion.

FIG. 8 is a sectional view showing a bead according to a secondembodiment of the present invention.

FIG. 9 is another example of protrusion formation.

FIG. 10 is a still other example of protrusion formation.

FIG. 11 is a yet further example of protrusion formation.

FIG. 12 is an additional example of protrusion formation.

FIG. 13 is a still further example of protrusion formation.

FIG. 14 is another example of protrusion formation.

FIG. 15 is yet another example of protrusion formation.

FIG. 16 is a still other example of protrusion formation.

FIG. 17 is a further example of protrusion formation.

FIG. 18 is an example that the base-plate bead is a half bead.

FIG. 19 is another example that the base-plate bead is a half bead.

FIG. 20 is a modification of a second elastic sealing material.

FIG. 21 is a plan view for explaining a conventional metallic gasket.

FIG. 22 is a sectional view taken along the line D—D in FIG. 21.

FIG. 23 is a diagram for explaining a conventional metal bead.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of the present invention will be described withreference to the drawings.

FIG. 1 is a plan view for explaining a metallic gasket according to thefirst embodiment of the present invention. FIG. 2 is a sectional viewtaken along the line A—A in FIG. 1. FIG. 3 is a sectional view takenalong the line B—B in FIG. 3.

Description will next be made of the structure of the metallic gasketaccording to the first embodiment.

A metallic gasket 1 according to the first embodiment is an embodimentof a cylinder head gasket for an internal combustion engine. A baseplate 20 of the metallic gasket 1 comprises thin metal plate, suchstainless steel plate, soft steel plate, or steel plate. Here, the firstembodiment will be described on the assumption that soft steel plate isused as a material for the base plate 20 with a view to providing a lessexpensive product.

As shown in FIG. 1, the base plate 20 is provided with a plurality ofcombustion chamber openings 2 aligned to each other in the longitudinaldirection, and a first thickness-increased portion 3 is formed byupwardly folding back the whole of the inner peripheral edge on the eachcombustion chamber opening 2 side of the base plate. The height of thefirst thickness-increased portion 3 is varied in its extendingdirection, such as by lowering the height at positions near bolt holes,to thereby equalize the surface pressure in the existing direction ofthe thickness-increased direction.

On the outer side of the first thickness-increased portion 3, there isprovided a first seal line SL1 in a manner to endlessly encircle thecombustion chamber opening 2 along the peripheral portion of thecombustion chamber opening 2. On the outer side of the first seal lineSL1, a plurality of cooling water holes 8 are arranged along theperipheral portion of each combustion chamber 2.

On the outer side of the plurality of the cooling water holes 8, asecond seal line SL2 is provided in a manner to encircle all of thecooling water holes 8. The second seal line SL2 is so arranged thatthere are no other holes than the cooling water holes 8 in the area ofthe base plate 20 which is located between the first seal line SL1 andthe second seal line SL2.

On the outer side of the seal line SL2, the bolt holes 6 are located. Anoil hole is denoted by reference numeral 7.

A third seal line SL3 is provided in a manner to encircle the bolt holes6 and the oil hole 7.

The seal lines SL1 to SL3 are integrated into a single common seal linewhere they run adjacent to one another.

A second thickness-increased portion 9 is formed by upwardly folding upthe outer peripheral edge of the base plate 20 at some parts of the baseplate 20. The height of the second thickness-increased portion 9 isarranged to be a little lower than the smallest height of the firstthickness-increased portion 3 by forging.

As shown in FIGS. 2 and 3, a bead BD is formed along the seal lines SL1to SL3. As shown in FIGS. 2 and 3, the bead BD in this embodiment isformed as a composite of a metal bead 4 or 5 and a rubber bead.

The metal beads 4, 5 in this embodiment are full beads formed by bendingthe base plate 20 so as to protrude on only one surface side (topsurface side) of the base plate 20 and the beads are arranged to behigher than the first thickness-increased portion 3. Therefore, when thebeads are elastically deformed in the through-thickness direction, asealing pressure can be generated.

The above-mentioned rubber bead comprises elastic sealing material parts11 a, 11 b, 13 a, 13 b fixed to the surface of the base plate 20 on theconvex portion side of the metal beads 4, 5, and elastic sealingmaterial parts 10 and 12 filled in the concave portion on the reverseside of the convex portion. The elastic sealing material parts 11 a, 11b, 13 a, 13 b, and 10, 12 may be formed by a corrosion-resistant,elastic material, e.g., a rubber material, such as fluororubber, NBR,silicon rubber, or a resin material.

The elastic sealing material parts 11 a, 11 b, 13 a, 13 b fixed to theconvex portion side of the metal beads 4, 5 are fixed to the surface ofthe base plate 20 in a manner to cover at least both sides across thewidth of the metal beads 4, 5. The height of the elastic sealingmaterial parts 11 a, 11 b, 13 a, 13 b fixed to the convex portion sideof the metal beads 4, 5 is made equal or substantially equal to theheight of the convex portion of the metal beads, and the top surface ismade substantially parallel with the flat surface of the base plate 20.The height of the elastic sealing material parts 11 a, 11 b, 13 a, 13 bmay be a little higher than the height of the convex portion of themetal beads 4, 5. Note, however, that the above-mentioned height of theelastic sealing material parts must be a height such that thecompression-deformed amount regulated by the height of the firstthickness-increased portion 3 is not more than 35% (the knowncompression-deformed amount of a specific material, which does not giverise to buckling).

On the other hand, the amount of the elastic sealing material parts 10and 12 filled in the concave portions of the metal beads 4, 5 is madesubstantially equal to the capacities of the concave portions and theirback surface is made substantially flush with the flat back surface ofthe base plate 20.

Description will next be made of the operation and the effect, etc. ofthe metallic gasket mentioned above.

When a metallic gasket 1 structured as described is disposed between theopposing joint surfaces of a cylinder block and a cylinder head andfastened with clamping bolts, the elastic sealing material parts 11 a,11 b, 13 a, 13 b and the elastic sealing material parts 10, 12 thatconstitute the rubber beads are compressed and deformed in thethrough-thickness direction in cooperation with the metal beads 4, 5,and at the end of fastening, the largest surface pressure concentrateson and the largest load acts on the first thickness-increased portion 3due to a difference in thickness between the first thickness-increasedportion 3 with the largest thickness of the base plate 2 and theremaining portions.

Therefore, a combustion gas at the highest pressure can be sealed by thefirst thickness-increased portion 3 pressed against the joint surface.On the outer side of the first thickness-increased portion 3, an areaseal is applied by an elastic resilience of the beads BD (metal beads 4,5 and rubber beads) formed along the first and second seal lines SL1 andSL2 as a shield against cooling water seeping out between the seallines.

And, as the largest compression-deformed amount of the beads BD isregulated by the first thickness-increased portion 3, a largest everspace, more specifically, a gap space SP corresponding to the clearanceof a piece of the whole base plate 20 is formed between the first sealline SL1 and the second seal line SL2, thereby increasing the coolingeffects of the metallic gasket 1. In other words, as a water pumppressure-feeds the cooling water into the gap space SP from a coolingwater hole 8, and the cooling water, while flowing, absorbs the heatgenerated by engine operation and transmitted from the engine, andsimultaneously cools the gasket 1, thus preventing the rubber beads ofthe gasket from deteriorating by heat.

At this time, the beads BD in this embodiment seal the joint surfaces bya composite spring force of the metal beads 4, 5 and the rubber beads,and since the sealing areas of the beads to contact the upper and lowerjoint surfaces are formed by the elastic sealing material parts 11 a, 11b, 13 a, 13 b and 10, 12, a small gasket factor can be set and thesealing can be applied by a low surface pressure, and even if thecompression-deformed amount is regulated to increase the amount of thegap space SP as described above, no problem arises.

Because the upper and lower sealing areas are the sealing areas by theelastic sealing material parts 11 a, 11 b, 13 a 13 b and 120, 12, ifthere are blowholes or the like on the joint surfaces, a sufficientsealing against water leakage can be obtained. Further, the rubber beadsare capable of sufficiently sealing the surface processing roughness orthe flaws that occur in transit.

As mentioned above, since a small gasket factor can be set for the beadsBD, no problem occurs if the base plate 20 is formed by low-hardnessless-expensive soft steel plate. The elastic sealing material parts 11a, 11 b, 13 a, 13 b and 10, 12 are used only on the upper and lowerportions of the bead lines required for sealing, and therefore theconsumed amount is small.

The metal beads 4, 5 are required only slightly higher than the heightof the first thickness-increased portion 3, and the height of the rubberbeads is set so as to be equal or slightly higher than the height of themetal beads 4, 5 in designing the mold, and therefore the processingaccuracy is stable. If the height of the metal beads is 30% higher thanthe first thickness-increased portion, the elastic sealing material doesnot suffer deformation fracture, generated load is a composite force ofthe metal beads of soft steel and the soft rubber beads and is thereforenot strong, and there is not such a large loss of load as to affects thesealing against the combustion gas pressure.

By varying the thickness in the circumferential direction of the firstthickness-increased portion 3, the sealing pressure is equalized andconsequently the fastening force of the bolts can be utilizedefficiently. As a result of the pressure being equalized in thecircumferential direction in the peripheral portion of the combustionchamber opening 2, the pressure of the joint surface in contact with thefirst thickness-increased portion 3 on the opening edge of thecombustion chamber (bore) is equalized in the circumferential direction,and therefore the roundness of the combustion chamber bore is preventedfrom being impaired by the imbalance of the sealing pressure at thefirst thickness-increased portion 3. The impairment of the roundness ofthe combustion chamber (bore) leads to increases in power loss and oilconsumption. Between the first and second thickness-increased portions3, 9 which receive a large proportion of the bolt fastening force, bymaking the second thickness-increased portion 9 relatively lower inthickness, the largest load may be applied to the firstthickness-increased portion 3 to thereby generate a high sealingpressure.

Since the base plate 20 is formed by soft steel plate of low hardness,it is easy to form the first thickness-increased portion 3 and thesecond thickness-increased portion 9 by bending.

The variation of the height of the first thickness-increased portion 3in the circumferential direction may be adjusted by forging, or as shownin FIG. 4, may be adjusted by inserting a shim plate 14 a into thefolded portion. When the shim plate 14 a is inserted in the foldedportion along the whole periphery of the first thickness-increasedportion 3, where there is the smallest thickness portion of the shimplate 14 a, the first thickness-increased portion 3 is at its smallestthickness. As a result, the height of the second thickness-increasedportion 9 can be made lower than the first thickness-increased portion 3without forging. In other words, setting the shim plate 14 a in thefirst thickness-increased portion 3 obviates the need to perform theforging to the second thickness-increased portion 9. The shim plate 14 aset in the first thickness-increased portion 3 increases the height ofthe first thickness-increased portion 3 by its thickness, and thereforethe gap space SP in which cooling water circulates can be made wider inproportion to the thickness of the shim plate 14 a, thus improving thecooling effects.

At this time, as shown in FIG. 5, a leaf spring 14 b elasticallydeformable in the through-thickness direction may be inserted as theshim plate 14 a into the first thickness-increased portion 3. In thiscase, in addition to the abovementioned effect, the surface pressure inthe circumferential direction of the first thickness-increased portion 3is equalized more readily by the elastic force of the leaf spring 14 b,and by this added spring of the first thickness-increased portion 3, thefirst thickness-increased portion 3 can follow after the thermaldeformation that occurs during engine operation, and consequently thesurface pressure equalization takes places in the firstthickness-increased portion 3 in a manner to follow the thermaldeformation.

In this embodiment, description has been made of the metal beads 4, 5 asfull beads, but as shown in FIG. 6, in the bead BD formed along thesecond seal line SL2, the metal bead 5 may be formed by a half bead. Inother words, in the areas where an available seal width is too narrow toprovide a full-bead 5, the metal bead 5 may be formed as a half bead tosuit the narrow seal width.

In this embodiment, description has been made of the thickness-increasedportion formed by folding back the base plate, but this is not intendedto give a definition of limits of the invention. For example, as shownin FIG. 7, the second thickness-increased portion 9 may be formed bywelding a thin plate thinner than the base plate 20 to the outerperipheral edge, thus obviating the necessity of forging mentionedabove. Or, the second thickness-increased portion may be formed byfolding back the peripheral portion of each bolt hole.

The sealing surface pressure by the metal beads 4, 5 may be equalized bypartly varying at least one of the protruding height and the width ofthe beads in their extending direction. For example, the protrusions ofthe beads are made relatively low or the bead width is made relativelynarrow in the vicinity of bolts. By equalizing the sealing pressure, thegasket can be sealed with high accuracy.

To the base plate part between the two beads BD along SL1 and SL2, acorrosion-resistant thin film may be fixed, which prevents rusting onthe surface of the base plate which always contact water.

A second embodiment of the present invention will be described withreference to the drawings.

The basic structure of this second embodiment is the same as that of thefirst embodiment, but slightly differs in the structure of the bead fromthe first embodiment.

Beads are formed along the seal lines SL1 and SL2.

As shown in FIGS. 8 and 9, the bead BD according to this embodiment is acomposite bead formed by a base-plate bead 6 as a full bead and rubberbeads 8, 10.

The base-plate bead 6 is formed by bending the base plate in thethrough-thickness direction and the base-plate bead 6 is formed convexthat is higher than the height of the thickness-increased portion 16.

The rubber bead comprises a first elastic sealing material part 10filled in the concave portion of the base-plate bead 6, and a secondelastic sealing material part 8 fixed to the convex portion side of thebase-plate bead.

The first elastic sealing material part 10 is arranged such that theunder surface of it is flat and flush with the under surface of the baseplate 2. Approximately in the center of the width direction of the beadand on the under surface of the bead, a convex protrusion 11 is formedalong the seal lines SL1 and SL2.

The second elastic sealing material part 8 is formed with a widthslightly wider than the width of the base-plate bead 6 and on thesurface of the convex portion of the bead and on the flat surfacecontinuous to the convex portion. The second elastic sealing materialpart 8 is designed so that its height is almost equal to the height ofthe base-plate bead 6 and the surface (the top surface) is substantiallyflat.

The width of the second elastic sealing material part 8 is preferablynot more than 1.5 times the width of the base-plate bead 6. If the widthis increased excessively, load increases excessively. The height of theelastic sealing material part 8 is preferably in the range of 0.9 to 1.1times the height of the base-plate bead 6.

The number and the kinds of holes, such as the bolt holes 4 formed inthe base plate 2, and the location of the seal lines SL1 and SL2naturally differ with the kind of a cylinder block and a cylinder headbetween which the metallic gasket 1 is disposed.

The metallic gasket 1 structured as described is set in place when it isdisposed between the joint surfaces of the cylinder block and thecylinder head of an engine and fastened with clamping bolts. The beadsare deformed by the fastening force of the clamping bolts and a requiredsealing pressure is generated along the seal lines to thereby seal oil,water and so on.

When the gasket is fastened, the thickness-increased portions 16provided at the peripheral end portion of the combustion chamber opening3 serve to limit the compression-deformed amount of the beads, a highsurface pressure occurs at the thickness-increased portions 16, so thatthe thickness-increased portion 16 seals a combustion gas at hightemperature and high pressure.

When no coating is applied to the surface of the thickness-increasedportion 16 to supply the gasket at a low price, the thickness-increasedportion 16 of the gasket comes into metal-to-metal contact with themachined surfaces (joint surfaces) of the engine, and consequently thereis a tool-mark irregularity of 3 to 6 microns on the machined surfaces.

The explosion pressure by engine operation is not a constantly-appliedpressure but a pulsating pressure; therefore, there is some pressureleakage from the thickness-increased portion 16 to the outer peripheryside. However, the pressure is sealed by the bead BD on the outer sideof the thickness-increased portion 16.

The bead BD according to this embodiment is so structured as to generatea required sealing pressure by a composite spring of the base-plate bead6 and the rubber bead produced when they are compressed and deformed,and this composite structure makes it possible to reduce the hardness ofthe base plate 2 that forms the base-plate bead 6. The beads contact theupper and lower joint surfaces at the flat surfaces of the compressedand deformed elastic sealing material parts 8 and 10, and the softelastic sealing material parts 8 and 10 come into tight contact with thejoint surfaces, closing any small spaces of the tool marks, therebysealing the combustion gas that leaks from the thickness-increasedportion 16 under pulsating pressure mentioned above.

In a gasket of a structure that an elastic sealing material is filledonly in the concave portion of the base-plate bead 6, when the elasticsealing material 10 is compressed and deformed, an external force isgenerated to deform the base-plate bead 6 and the flat portion on eachside continuous to the base-plate bead 6 in such a manner that they warpupward. The lower the hardness of the base plate 2 is made to inhibitfatigue failure of the base-plate bead 6 and hold down the cost of thebase plate 2, the more conspicuous the deformation, such as upward warpis likely to become. However, in this embodiment, the second elasticsealing material 8 is provided also on the convex portion side and thesecond elastic sealing material 8 is deformed to prevent deformation ofthe base-plate bead 6 and the base plate 2, thereby preventing thedeterioration of the seal performance by the first elastic sealingmaterial 10 in the concave portion.

In the filling of the first elastic sealing material 10, the centerportion of it is likely to cave in a little in a transition from hightemperature to open cooling. In this embodiment, protrusions 11 and 9are formed on the above center portion, even when the gasket is adoptedin an engine whose fastening axial tension is weak, a stable sealperformance can be secured at low lost in the region on the outer sideof the combustion chamber opening 3. After the bolts are fastened, theprotrusions 11 and 9 are in a crushed and flattened state.

No fastening problem arises in the vicinity of bolts 4 is free of aslong as the bolts are fastened properly. However, the oil holes 5 andthe chain chamber hole 17 are in an improperly fastened state becausethey are remote from clamping bolts. As the engine is subjected torepeated thermal cycles as many times as it is used, the fastening axialtension decreases to some extent. The gasket is deformed by heat duringengine operation, thus aggravating the sealing condition.

In order to implement a complete seal under those adverse conditions, inthe prior art, in the bead structure having the elastic sealing materialfilled in the concave portion of the base-plate bead, if the hardness ofthe base plate 2 is increased, the spring force is increased, but thebead may suffer fatigue failure by vibration amplitude, and it is notdesirable to increase the hardness so much; on the other hand, if thehardness of the base-plate bead 6 is decreased, deformation mentionedabove will occur, resulting in a decrease in the spring force. To makeup for this shortcoming, in this embodiment, as described above, inaddition to the first elastic sealing material 10 filled in the concaveportion of the base-plate bead 6, the second elastic sealing material 8is formed on the convex portion on the reverse side of the concaveportion, and the second elastic sealing material 8, structured such thatits width is wider than the width of the bead and its height issubstantially the same height of the base-plate bead 6, serves toprevent deformation of the base plate 2 and the base-plate bead 6.

As the hardness of the base plate 2 is lowered, the spring force is madelow, but because the first elastic sealing material 8 is formed, on theconvex portion, with a height equal to the height of the base-plate bead6 to thereby regulate the deformation by the elastic sealing material 10filled in the concave portion, with the result that the BD bead isprovided with a spring force equal to or greater than a spring force bya structure that uses the base plate 2 of a high-hardness material.

Further, when the elastic sealing material 10 is formed by molding, theconcave portion side of the base-plate bead 6 is processed so as to beflush with the flat surface of the base plate 2. During molding, thesealing material 10 expands thermally by high temperature, but when itis open-cooled, the central portion of the rubber large in thicknessshrinks by an amount corresponding to thermal expansion, and caves inslightly, and in the portions, away from a clamping bolt, which are notfastened properly and overhang, the surface pressure may decrease,leaving chances of pressure leak.

As countermeasures, according to the invention in this patentapplication, as shown in FIG. 8, a small protrusion 11 is formed in themiddle of the surface of the elastic sealing material 10 in the concaveportion of the base plate 6, the bead is deformed without increasing thefastening load so much, and when the surface pressure decreases, theprotrusion 11 formed on the surface of the first elastic sealingmaterial 10 bulges and deforms concurrently. Though small in terms ofarea, the protrusion generates a high surface pressure, and serves toapply a complete seal. In other words, located in a position away fromthe clamping bolt to the outer circumference side, the surface pressuretends to become relatively small, the elastic sealing material on bothsurfaces of the base-plate bead 6 is normally pressed to the opposedjoint surfaces to seal them by the compressed and deformation of thebead by the fastening load. At this time, the protrusion 11 formed onthe elastic sealing material 10 on the concave portion side is deformedin a manner to be pushed into the concave portion, adapts itself to theflat surface of the joint surface, and becomes substantially flush withthe flat surface (underside) of the base plate 2.

When, from this steady state, the clearance between the opposed jointsurfaces at the bead position increases by vibration, for example, thesurface pressure temporarily decreases, the compression-deformed amountof the bead decreases, thus reducing the sealing pressure. At theelastic sealing material 10 on the concave portion side, according to anincrease in the clearance, the protrusion 11 automatically bulges tosecurely retain contact with the opposite joint surface and has thecontact surface decreased, and can maintain the seal condition by anincrease in the surface pressure by the protrusion. As the clearancedecreases, the steady state is restored.

In the foregoing, description has been made of a case where the surfacepressure decreases with changes in the clearance between the opposedjoint surfaces. Even when the clearance between the opposed jointsurfaces remain unchanged or even when the spring force decreases withdeterioration with time and the surface pressure becomes smaller, asdescribed above, because load concentrates on the protrusion 11 as thesurface pressure decreases (the protrusions 11 and 9 do not necessarilybulge in this case), the surface pressure rises at the position of theprotrusion 11, making it possible to maintain a specified sealingpressure.

When the change in the gap at the bead position between the jointsurfaces is large, it is preferable to form a protrusion 9 also on theelastic sealing material on the convex portion of the base-plate bead 6as shown in FIG. 10.

The protrusions 11, 9 arranged in the bead-width direction are notlimited to one, and may be two or more as shown in FIGS. 11 to 13. Whentwo or more protrusions are provided, the height of the protrusions 11,9 may be made different. The magnitude of the protrusions may also bedifferent. When a plurality of protrusions are formed, load of surfacepressure can be alleviated, or if the surface pressure decreases, alabyrinth effect may be obtained by the plurality of protrusions 11, 9or the de facto increase of the seal lines SL provides an effect of astable sealing property for an extended period of time.

Further, with regard to the plurality of protrusions 11, 9, by makingvariations in the size or shape (the area unit length in a longitudinalsectional profile or a plan view) of the protrusions 11, 9 to seekoptimization of the protrusions 11, 8 as shown in FIGS. 31 to 34, it ispossible to enlarge the above-mentioned effects. In other words, whenproviding two or more protrusions in parallel widthwise, it ispreferable to make the height of the protrusions 11, 9 relatively low orreduce the area per unit length on the higher surface pressure side.

With regard to a single-line protrusion 11, 9 extending along the sealline, it is possible to change the height or shape of the protrusion 11,9 according to the surface pressure at the location of the protrusion11, 9. In other words, in the areas where the surface pressure isrelatively smaller, the height and the width of the protrusion 11, 9 maybe increased.

The protrusions 11, 9 may be formed continuously along the whole lengthof the seal lines SL1 and SL2 or intermittently at specified intervals.

When the protrusions 11, 9 are formed partly on the seal lines SL1, SL2,they should be formed at positions that are far from the bolt hole andat relatively low surface pressure or at parts where changes in theclearance between the opposed joint surfaces are relatively large (theamplitude of surface pressure change is relatively large).

In this embodiment, description has been made of the base-plate bead 6as a full bead, but this embodiment is applicable when the base-platebead 6 is a half bead in a stepped structure. More specifically, asshown in FIGS. 18 and 19, a second elastic sealing material 12 is fixedto the convex portion (the portion rising from the flat part of the baseplate) of the base-plate bead 6 in a stepped form, a first elasticsealing material 14 is applied to the concave portion on the reverseside of the convex portion, and then protrusions 13, 15 are formed atthe thick portions. The operation and the effect are the same as in theabove-mentioned embodiment.

In the bead BD in the vicinity of the thickness-increased portion 1, thesecond elastic sealing material need not necessarily be attached to bothsloped sides of the convex portion as shown in FIG. 20. In other words,receiving a relatively high surface pressure and having a strong forceto constrain the base plate, the thickness-increased portion 16 inhibitsthe base plate from being deformed. This applies to the portions in thevicinity of clamping bolts.

The height of the protrusions 11, 9 should be designed such that thedeformation ratio is not more than 25% when the protrusions are deformedto reach the thickness of the thickness-increased portion 16, regardlessof the shape of protrusions.

In the above example, description has been made of a metallic gaskethaving a single base plate. In a metallic gasket, a plurality of baseplates, each having the above-mentioned structure, may be stacked oneover another according to the space between the joint surfaces. In thiscase, the base plates need not necessarily be stacked such that theconvex portions of the base-plate beads are arranged face-to-face witheach other as in prior art.

The other aspects of the structure, the operation and the effect are thesame as in the above-mentioned embodiments.

INDUSTRIAL APPLICABILITY

As has been described, by adopting the present invention, the processingaccuracy of the metal beads can be improved and the cooling effects canbe increased on the metallic gasket itself and the joint surfacesbetween which the metallic gasket is sandwiched.

1. A metallic gasket comprising a base plate made of a thin metal plate,said base plate having at least a combustion chamber opening and acooling water hole, and having a first thickness-increased portion madeof metal and increased in thickness and encircling a peripheral edge ofsaid combustion chamber opening, a first bead formed on the outer sideof said first thickness-increased portion of said base plate in a mannerto endlessly encircle said combustion chamber opening, and a second beadformed on the outer side of said first bead in a manner to endlesslyencircle said combustion chamber opening and said cooling water hole,wherein in a region of said base plate between said first bead and saidsecond bead, there are no holes other than said cooling water hole, andeach of said first and second beads is a composite bead of a metal beadand a rubber bead, wherein said metal bead is formed only on one surfaceside of said base plate by bending said base plate in athrough-thickness direction to create a convex portion higher than theheight of said first thickness-increased portion, wherein said rubberbead is formed of an elastic sealing material fixed to said convexportion side surface of said metal bead and filled in a concave portionon the reverse side of said convex portion and said rubber bead iscompressed and deformed in the through-thickness direction incooperation with deformation of said metal bead, and wherein saidelastic sealing material on the surface of said convex portion side isfixed at least to the surface of said convex portion of said metal beadand is arranged to have a height equal or substantially equal to theheight of said metal bead, further a second thickness-increased portionis provided at an outer peripheral edge of said base plate.
 2. Ametallic gasket according to claim 1, wherein to equalize said surfacepressure when said gasket is sandwiched between said joint surfaces, theheight of said first thickness-increased portion is varied partly andthe height of said second thickness-increased portion is lower than thelowest height of said first thickness-increased portion.
 3. A metallicgasket according to claim 2, wherein said first thickness-increasedportion is formed by folding back a peripheral edge on said combustionchamber opening side of said base plate, and a shim is fitted into saidfolded portion to thereby adjust the height of said firstthickness-increased portion.
 4. A metallic gasket according to claim 2,wherein said first thickness-increased portion is formed by folding backthe peripheral end on said combustion chamber opening side of said baseplate, and a leaf spring for spring action in the through-thicknessdirection is inserted in said folded portion.
 5. A metallic gasketaccording to claim 2, wherein by partly varying at least one of a heightof a protrusion and a width of said beads in the extending directionthereof, said sealing surface pressure by said beads is equalized in anextending direction thereof.
 6. A metallic gasket according to claim 2,wherein a thin corrosion-resistant film is fixed to that portion of saidbase plate located between said first bead and said second bead and atleast on the surface of said convex portion side of said metal beads onsaid base plate.
 7. A metallic gasket according to claim 2, wherein oneor not less than two lines of protrusions are provided along the seallines of said sealing material, on at least either on one of the surfaceof said elastic sealing material fixed to the surface of said convexportion side and the surface of said elastic sealing material filled insaid concave portion, said sealing material being used to constitutesaid rubber beads.
 8. A metallic gasket according to claim 2, whereinone line or not less than two lines of protrusions are provided wherethe sealing pressure is relatively low on at least one of the surface ofsaid elastic sealing material fixed to the surface of said convexportion side and the surface of said sealing material filled in saidconcave portion of said base plate, said sealing material being used toconstitute said rubber beads.
 9. A metallic gasket according to claim 7,wherein in the above-mentioned lines of protrusions, at least one of theheight of said protrusion and the width in the extending directionthereof is varied according to said sealing pressure at formed positionssaid protrusions, and at least one of the height of said protrusion andthe width is set at a larger value where said sealing pressure is lower.10. A metallic gasket according to claim 7, wherein a plurality ofprotrusions are provided on at least one of the surface of elasticsealing material fixed to the surface of said convex portion side andthe surface of said elastic sealing material filled in said concaveportion of said beads, and in said plurality of protrusions, at leastone of an area per height of protrusion and a unit length is variedaccording to said sealing pressure at formed positions of protrusions.11. A metallic gasket according to claim 7, wherein a plurality of baseplates are stacked in a multilayered structure.